Pass Config pointer into AuthManager

AuthManager needs to have logic for re-claming devices. This requires
persistent storage for secret and owner. It's going to be easier to
handle logic there than outside.

BUG=25766815

Change-Id: Icc417f23715b48461098503fd241cee534d2225c
Reviewed-on: https://weave-review.googlesource.com/1949
Reviewed-by: Vitaly Buka <vitalybuka@google.com>
diff --git a/src/device_manager.cc b/src/device_manager.cc
index cb575b8..88256da 100644
--- a/src/device_manager.cc
+++ b/src/device_manager.cc
@@ -33,15 +33,8 @@
   config_->Load();
 
   if (http_server) {
-    auth_manager_.reset(
-        new privet::AuthManager(config_->GetSettings().secret,
-                                http_server->GetHttpsCertificateFingerprint()));
-
-    if (auth_manager_->GetSecret() != config_->GetSettings().secret) {
-      // There is no Config::OnChangedCallback registered.
-      Config::Transaction transaction(config_.get());
-      transaction.set_secret(auth_manager_->GetSecret());
-    }
+    auth_manager_.reset(new privet::AuthManager(
+        config_.get(), http_server->GetHttpsCertificateFingerprint()));
   }
 
   device_info_.reset(new DeviceRegistrationInfo(